System Operations Improvements

Operational flexibility is the ability of a power system to respond to changes in electricity demand and generation. Well-designed system operations help to extract flexibility from the existing physical infrastructure and can often be implemented at lower economic costs than options that require changes to the physical power system. Other sources of flexibility include: 1) expanding a power system’s balancing area; improving forecasting; and increasing thermal plant cycling capability.

Introduction

Operational flexibility is the ability of a power system to respond to changes in electricity demand and generation. Operational flexibility is a prized characteristic in power systems, particularly those with significant variable renewable energy (RE). While system operators have many tools at their disposal to unlock flexibility (e.g., flexible generation, transmission, storage, demand response, and power markets), changes to system operational practices are among the most readily accessible interventions. Well-designed system operations help to extract flexibility from the existing physical infrastructure and can often be implemented at lower economic costs than options that require changes to the physical power system.

For example, adjusting day-ahead generation scheduling practices to allow changes closer to real time allows dispatch decisions to be made based on improved forecasts of both variable RE output and demand. This decreases the need for expensive reserves and allows more accurate and efficient market operation.

Other examples of institutional and operational sources of flexibility include:

Expanding a power system’s balancing area to provide access to geographically diverse wind and solar resources and diverse demand;

Improving wind and solar forecasting; and

Increasing thermal plant cycling capability.

Example Interventions

System operations can be improved to facilitate integration of variable RE through the following actions:

Expand sub-hourly dispatch and intra-hourly scheduling. Shorter intervals allow for a more efficient response from grid operators as load forecasts and variable RE forecasts are more accurate closer to dispatch.

Improve weather, wind, and solar forecasting, for example, by:

Utilizing more accurate data;

Calibrating the forecasts against actual experience to identify forecasting errors; and

Enabling system operators to use forecasts frequently to inform commitment and dispatch decisions.

Take advantage of geographic diversity of variable RE resources to smooth variability by expanding the balancing area footprint and/or coordinating with other balancing areas.

Update grid codes to incorporate requirements for wind turbines to provide active power controls, such as fault ride-through, reactive power, and potentially automatic generation control, inertial response, and primary frequency response. An assessment of whether these services can improve reliability and are economical is a necessary pre-requisite.

Reading List and Case Studies

National Renewable Energy Laboratory, University of Colorado, Electric Power Research Institute, 2014

This study explores technologies that can provide control of active power output from wind power. The study assesses how active power control technologies impact production costs, wind power revenue streams, and the overall reliability and security of the power system. The authors find that wind turbines have great potential to provide automatic power controls. However, careful market and control system design will be needed to realize these benefits.

This report discusses system operations and investment in liberalized electricity markets in which greater variable RE and energy efficiency resources are being deployed. It overviews current and foreseen challenges and possible policy and regulatory solutions to improve the cost efficiency and flexibility of the grid. Chapter 3 (pg. 36) outlines operational challenges associated with significant variable RE penetration.

This report, commissioned by the Western Governors’ Association in the United States, provides an assessment of system operational measures that could reduce costs of wind and solar integration to the end-users. The report identifies challenges to adopting these measures and recommendations for action at the state level. Especially useful are the high-level and accessible explanations of these operational measures.

This report summarizes effective actions that countries have taken to integrate significant variable RE. It includes detailed case studies such as how Australia and Spain each developed and integrated advanced forecasting techniques (pg. 49 and 105), and how Spain allowed for larger balancing areas (pg. 104). The report explores additional topics and case studies, including Ireland, Denmark, Germany, and the United States.

This report reviews grid interconnection codes that relate to the performance of wind turbines, as well as requirements that can validate wind farm and turbine performance. Also reviewed are modeling requirements for simulating the performance of wind farms in the power system. Specifically, the authors examine grid codes from the UK, Germany, Denmark, Spain, Texas, Canada, and Europe.

This report details case studies of Spain, Germany, Denmark, and several balancing areas in North America and looks at the specific systems operational measures undertaken to integrate variable RE. The case studies examine how systems operators improved their situational awareness, ability to assess real-time reliability and risks, and decision support processes.

Regulatory and Policy Examples

This manual includes the instructions, rules, procedures and guidelines that were established by the PJM regional transmission operator to support operations, planning, and accounting for both the regional transmission system and the PJM energy market.

ENTSO-E defines a common set of minimum requirements for the European-wide power system. The requirements include load-frequency control and reserves principles to ensure the operational security of the system and cross-border cooperation between transmission system operators. The requirements may also dictate the characteristics of the grid-connected systems, consumption, and distribution systems. The code addresses the load-frequency structure, operational rules, quality criteria, reserve dimensions and exchange, sharing and distribution, and monitoring.

European Network of Transmission System Operators for Electricity (ENTSO-E), 2012

This document outlines the process ENTSO-E has undertaken to develop network codes that define security and reliability, connection, third-party access, data exchange and settlement, interoperability, operational procedures in an emergency, capacity allocation and congestion management, trading and related technical and operational provisions, transparency, balancing, harmonizing transmission tariff structures, and energy efficiency. The network codes’ characteristics, the role within the development process, the process itself, interpretation of the rules, and a process for maintaining the codes are included.

This manual provides detailed guidance for the facilities and controls maintained by the New York Independent System Operator, a regional transmission operator. It includes sections on operations monitoring, transmission operations, scheduling operations, and dispatching operations for all generation types.

Order 888 mandates that electrical services and marketing functions be disaggregated and requires utilities to provide open access to their energy rate schedules. The order also makes provisions for conventional utilities to recover stranded costs and for transmission owners to offer their services on the open market.

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Interested in partnering through Greening the Grid to receive technical assistance on grid integration? Please contact us (greeningthegrid@nrel.gov) to learn more and explore opportunities for collaboration.

Greening the Grid is supported by the U.S. Agency for International Development (USAID), and is managed through the USAID-NREL Partnership, which addresses critical aspects of advanced energy systems including grid modernization, distributed energy resources and storage, power sector resilience, and the data and analytical tools needed to support them.